Following McDowel et. al. [1]} the local fluctuations
\(\tilde{\delta }^{i}_j = \delta ^{i}_j/\Delta \)  may be rewritten as:
\( \tilde{\delta }^{i}_j = \frac{1}{k_{max}-k_{min}} \sum _{k=k_{min}}^{k_{max}}\sqrt{2 F^i_k} \cos (\mathcal {K} j + \phi ^i_k),\) 
